The present disclosure generally relates to an amplifier and, more particularly, to the auto-zero amplifier and relevant circuits.
Sensors are widely adopted in many applications for detecting small signals. The detected signals are amplified for further signal processing. For example, the Hall effect sensor is often used for detecting the magnetic field. The Hall effect sensor may, however, only generate a few microvolts of detected signal when the detected magnetic field is one Gauss. When the detected signals are amplified by the amplifiers, the offset voltage of the sensor (e.g., the Hall Plate), the offset voltage of the amplifier, and the noise in the circuits are often much greater than the detected signals. Therefore, the amplified detected signals are no longer accurate.
The auto-zero amplifier is one of the amplifier architectures specific to processing small signals. In the auto-zero amplifier, the amplified signals and other offset voltages are stored in a plurality of capacitors (e.g., two or four capacitors). The signals stored in the capacitors are summed or subtracted to cancel out the offset voltages, and the amplified signals generated by the auto-zero amplifier may be more accurate.
Nevertheless, it takes time for charging the capacitors in the auto-zero amplifier. If there are many capacitors or the capacitances of the capacitors are large, the charging time will be even elongated accordingly. Thus, the auto-zero amplifier may not function normally when input signals vary too fast. The response time, the bandwidth, and the operation frequency of the auto-zero amplifier is therefore limited.